Jumps in Alfa's power levels
with long recovery times (greater than seconds) has been seen for some
time (see alfa
pwr jumps). During the painting project alfa was brought down to
the lab to be worked on. After reinstalling alfa in the dome,
test were done with the pdev spectrometer to measure the power jumps.
The setup was:

Send the 300 MHz of alfa into 2 170 MHz bands of the pdev
spectrometer. The first IF was centered on 1375 MHz (first lo=
1375+250=1625.). One of the 170 MHz bands was centered at 1300 MHz and
while the other was centered at 1450 MHz.

The telescope was parked at a particular position (say 340,18
were faa is strongest) or it was driven at a constant rate (either in
za or az).

Processing the data:

The idl routines masrdrsat and masrdrsatplt were used to
process and plot the data.

For each scan the total power for the 1450 MHz band was computed
and then normalized to the median value.

The peak spectral value for the 3 radars was recorded each 200
usecs. The search was done for 1 MHz or 3 channels (whichever was
longer) about the radar frequencies. PolA and PolB were searched
simultaneously. The frequencies used were:

FAA:1330,1350 MHz

REMY:1270,1290 MHz

AeroStat: 1241.74,1256.5,1246.2,1261.25 MHz

Often the aerostat was not running but we still got a signal
since the punta Salinas radar also uses some of these frequencies. You
can tell the punta Salinas radar by the longer blanking (3versus 1.4
secs) and the extra short blanking for the san juan airport radar
(5.5 seconds after the end of the AO blanking).

Data covering the entire time was plotted:

Each beam is plotted in a different color.

The 1450 (clean) band was smoothed to 20 milliseconds. Offsets
were included for plotting.

For each radar the peak power over 20 milliseconds was plotted
in db above Tsys.

Higher resolution about any compression was also plotted:

The 1450 band usually showed a jump in some beams as well as
positive going spikes that are intemods/harmonics of the faa radar.

The radar peak powers are also shown during the compression
event.

Dynamic range.

The maximum dynamic range for
the radar peaks varied from 35 to 45 db above Tsys. This is the ratio
of the Peak radar power in 1 channel vs the average power in a channel.
To get the increase in total power divide this increase by the number
of channels (usually 128 for 1 single 170 MHz band). This doesn't take
into account multiple radar frequencies (eg 1330,1350) or that there
are
2 170 MHz bands.

For early datasets, the compression is probably occurring in
the pdev mixer chassis. This depended on the attenuation and input
level used to the pdev device.

Comments:

Alfa still has a problem with a power jump and long recovery time
when the faa radar points at AO.

There was no tsys increase and then long recovery for
az=285,za=10. It was present for all of the az=340,za=18 positions.

At az=340,za=18 beam 3 always had the jump and slow recovery.
Beams 2 and 4 sometimes had it. This is probably a geometry problem.
Moving in az,za would probably cause another beam to have the problem.

The spacing of the 2 millisecond dips lined up with the faa ipps.

The 1330,1350 radars are causing intermods/harmonics in the 1450
MHz band at 135.02,1474.94, and 1480.33

Two za strips were done at az=180. 2->19.5 degrees
followed by 19.5->2 degrees. The dome moved at .02 degrees/second.
The 1450 band data was smoothed and then decimated to .2 seconds. The
radar bands had peak holds done over the same time step. The radars
rotate at 12 seconds. In this time the za moved by .02*12 = .24
degrees. The repeatability will be limited by this value ( the za
position of compression going up will be a little different than the za
position of the compression going down.
During the data taking the Remy and aerostat radars
were running. The faa radar was off. No compression was seen in the
entire dataset.
The plots are:

Data was taken at 4 settings of the alfa rotation
angle: 19,0,40 and 60 degrees to see how the jumps moved from beam to
beam. When rotating from 0 to 60 degrees, beams N -> N-1 so you
might expect to see the jumps move from beam to beam. A 60 degree
rotation moves 1 beam to the next, but the waveguide probes are not at
the same angle as the previous beam.

rotAngle 0 .. jumps beams 0,1,2,3,4.. 2 and 4 the strongest

rotAngle 19 ..jumps in beams 3,4

rotAngle 40 .. jumps in beams 1,3,4,5

rotAngle 60 .. jumps in beams 0,1 3,4 5 3 and 5 the
strongest

The the rotation from 0 to 60 degrees mapped the
strongest compressions 2,4 -> 3, 5 which was expected.processing: x101/080318/rdrsatrot.pro

The dome moved at .02 degrees/second. The 1450 band
data was smoothed and then decimated to .2 seconds. The radar bands had
peak holds done over the same time step. The radars rotate at 12
seconds. In this time the za moved by .02*12 = .24 degrees. The
repeatability will be limited by this value ( the za position of
compression going up will be a little different than the za position of
the compression going down.
Jumps in the total power (with long recovery times
> secs) were seen. The data is plotted vs za. When moving down in
za, the jumps are from the right to left in the plots.When moving up
the jumps go from small to larger za.
During the data taking the Remy , punta Salinas, and
FAA radar were running. The Aerostat radar was off. Peaks in the
aerostat plots are from the punta Salinas radar (which shares the
same frequencies).
The plots are:

Compression was seen in the up down directions when the azimuth was at
360. It was not seen when the za swings were at an azimuth of 180. All
of the jumps lined up with just the FAA radar.

Za
locations for saturation during za strips

za
Deg

az
Deg

direction

Beams
with
Saturation

maximum
strength

3.0

360

up

5

<1%

5.45

360

down

3,4

1%

5.55

360

up

3,4,5

1%

6.15

360

down

4

<1%

6.29

360

up

3,4

2%

6.4

360

down

3,4,5

2%

13.87

360

down

3,4

1%

13.97

360

up

3.45

2%

17.23

360

down

3,4

4%

17.35

360

up

2,3,4,5

1%

Daily Summary:

Jumps with long compression were see during za strips
(2->19.5) when the azimuth was positioned at 360 Degrees.

No jumps were seen when the azimuth was at 180 degrees.

Jumps were repeatable when moving up and moving down (within the
.24 degrees of the 12 second radar rotation). This says that the
problem is not being caused only be a glint from a plane. It is there
all the time (as long at the radar points at us).

The jumps are being caused by the FAA radar. They are not being
caused by the remy or punta Salinas radar.

When the jumps occur, the faa peak power is not a narrow function
of za when moving at .02 deg/sec.